The present invention relates to a cooling-air nozzle which comprises essentially a nozzle body with inlet and outlet orifices for the film-cooling of heated surfaces, in particular for use with flame tubes in the combustion chambers of gas turbines.
As the hot gas temperatures in the combustion chambers of gas turbines rise, convective cooling of the flame tubes becomes increasingly more difficult. To obtain uniform cooling of the flame tube, it is necessary to provide film-cooling wherein a film of cooling air flows along the wall of the flame tube on the side of the flame or the hot gas, which film of cooling air prevents the hot gases from coming into direct contact with the wall. The wall temperatures can effectively be lowered in this way.
Among the various proposals which have already been made for carrying out the film-cooling of flame tubes are, for example, the provision of orifices bored directly into the wall, or the provision of apertured rings inserted into the wall of the flame tube (see page 52 of Sawyer's Gas Turbine Catalog, 1976).
These known solutions involve, however, the disadvantages that the resulting film of cooling air is interrupted and that heat stresses arise in the ring portions due to an uneven temperature distribution. Moreover, the provision of orifices or apertured rings in the shell of the flame tube can lead to burbles in the flow of hot gas.
It is, therefore, an object of the present invention to minimize or obviate problems of the type discussed above.
It is another object of the present invention to provide a cooling-air nozzle in which the known disadvantages do not arise and in which the film of cooling air achieves a uniform surface cooling of the wall of the flame tube.